Effects of compost and phosphate amendments on arsenic mobility in soils and arsenic uptake by the hyper

Trang 1

Eﬀects of compost and phosphate amendments on arsenic mobility

in soils and arsenic uptake by the hyperaccumulator,

Pteris vittata L.

Xinde Caoa, Lena Q Maa,* , Aziz Shiralipourb

a Department of Soil and Water Science, University of Florida, Gainesville, FL 32611, USA

b Center for Natural Resources, University of Florida, Gainesville, FL 32611, USA

Received 21 February 2003; accepted 26 May 2003

‘‘Capsule’’: Phosphate amendment increases the eﬀectiveness of Chinese brake fern to remediate As-contaminated soils,

by increasing As uptake and decreasing As leaching

Abstract

Chinese brake fern (Pteris vittata L.), an arsenic (As) hyperaccumulator, has shown the potential to remediate As-contaminated soils This study investigated the eﬀects of soil amendments on the leachability of As from soils and As uptake by Chinese brake fern The ferns were grown for 12 weeks in a chromated–copper–arsenate (CCA) contaminated soil or in As spiked contaminated (ASC) soil Soils were treated with phosphate rock, municipal solid waste, or biosolid compost Phosphate amendments sig-niﬁcantly enhanced plant As uptake from the two tested soils with frond As concentrations increasing up to 265% relative to the control After 12 weeks, plants grown in phosphate-amended soil removed > 8% of soil As Replacement of As by P from the soil binding sites was responsible for the enhanced mobility of As and subsequent increased plant uptake Compost additions facilitated

As uptake from the CCA soil, but decreased As uptake from the ASC soil Elevated As uptake in the compost-treated CCA soil was related to the increase of soil water-soluble As and As(V) transformation into As(III) Reduced As uptake in the ASC soil may be attributed to As adsorption to the compost Chinese brake fern took up As mainly from the iron-bound fraction in the CCA soil and from the water-soluble/exchangeable As in the ASC soil Without ferns for As adsorption, compost and phosphate amend-ments increased As leaching from the CCA soil, but had decreased leaching with ferns when compared to the control For the ASC soil, treatments reduced As leaching regardless of fern presence This study suggest that growing Chinese brake fern in conjunction with phosphate amendments increases the eﬀectiveness of remediating As-contaminated soils, by increasing As uptake and decreasing As leaching

Published by Elsevier Ltd

Keywords: Phosphate; Biosolid compost; Municipal solid waste; Arsenic mobility; Arsenic uptake; Chinese brake fern; Remediation

1 Introduction

Arsenic (As) has long identiﬁed as a carcinogen

Ele-vated concentrations in the ecosystem is of great

con-cern for public health and the environment (Hingston et

al., 2001) Arsenic contamination in soils results from

various human activities including milling, combustion,

wood preservation, and pesticide application (

Carbo-nell-Barrachina et al., 1998) There are tens of

thou-sands of arsenic contaminated sites worldwide, with the

arsenic concentration as high as 26.5g kg 1soil ( Hing-ston et al., 2001)

Inorganic waterborne preservatives, such as chro-mated copper arsenate (CCA), are eﬀective in protecting wood from bacterial, fungal, and insect attacks ( Hing-ston et al., 2001) However, broad use of CCA in treat-ing wood has increased concerns about possible environmental contamination from the leaching losses

of wood preservatives As arsenic accumulates in soils, there may be an increase in health risks resulting from

As leaching into ground and surface water and sub-sequent consumption by animal and human popula-tions A recent report by the National Research Council concluded that the former arsenic standard of 50 mg l l

0269-7491/03/$ - see front matter Published by Elsevier Ltd.

doi:10.1016/S0269-7491(03)00208-2

www.elsevier.com/locate/envpol

* Corresponding author Tel.: 352-392-1951 ext 208; fax:

+1-352-392-3902.

E-mail address: lqma@uﬂ.edu (L.Q Ma).

Trang 2

in drinking water does not achieve USEPA’s (United

States, Environmental Protection Agency) goal of

pro-tecting the public health (Christen, 1999) In response to

this research, USEPA has lowered the drinking water

standard from 50 to 10 mg l l, eﬀective nationally by

2006

Arsenic-contaminated soil is one of the major sources

of arsenic in drinking water (Hingston et al., 2001)

Therefore, to protect animal and human health,

remediation of the contaminated sites has become an

urgent issue Phytoremediation, a plant-based green

technology, has been successfully used to remove a

number of metals from contaminated soils (Lombi et

al., 2001) Chinese brake fern (Pteris vittata L.) has

been recently discovered to be an arsenic

hyper-accumulator (Ma et al., 2001) The plant has

accu-mulated up to 2.3% As of dry plant weight from

contaminated soils Phytoremediation is feasible since

90% of the arsenic absobed was in the above-ground

biomass, and could be removed by frond harvest (Tu

et al., 2002)

A key to eﬀective phytoremediation, especially

phy-toextraction, is to enhance pollutant phyto-availability

and to sustain adequate pollutant concentrations in the

soil solution for plant uptake (Lombi et al., 2001)

Var-ious soil amendments have been used to aid plant

uptake and accumulation of contaminants (Heeraman

Incorporation of carbon-rich composts into soils has

been shown to increase metal solubility through

forma-tion of soluble metal–organic complexes (Zhou and

found that As adsorption by humic materials depends

on soil pH with a maximum sorption at pH of 5.5 But

arsenic can also be transformed to the reduced As(III)

species or organic forms through biomethylation by

microbes over a wide range of pHs (Turpeinen et al.,

1999) Reduced compounds have higher mobility than

As(V) forms, possibly enhancing their plant availability

Phosphate addition to arsenic-contaminated soils has

been shown to enhance arsenic release from the soil

through competitive anion exchange (Peryea and

Kam-mereck, 1997) Peryea (1998) reported that phosphate

fertilizer increased soil As availability to apple trees

grown in As- contaminated soils

With the appeal of increased arsenic availability from

the application of compost and phosphte for

phytor-emediation, there is also the concern for ground water

quality As arsenic availability is increased by soil

amendments, it is hoped that the Chinese brake fern

will proportionally absorb the available arsenic and

minimize arsenic leaching However, whether the

increased plant will balance leaching from the top soil

remains unclear

The overall objective of this study was to determine

whether soil amendments could increase arsenic uptake

by the Chinese brake fern while avoiding leaching los-ses The special tasks were: (1) to evaluate the eﬀects of composts and phosphate rock applications on arsenic uptake by Chinese brake fern growing in arsenic con-taminated soils; (2) to determine the eﬀects of composts and phosphate rock on arsenic leachability in arsenic contaminated soils; and (3) to identify possible mechanisms responsible for As mobility in soil after compost and phosphate treatments

2 Materials and methods 2.1 Soil, compost and phosphate rock samples The As-contaminated soil was collected from the sur-face (0–20 cm) at an abandoned CCA wood preserva-tion site, located in north central Florida A non-contaminated soil was taken from the surface (0–20 cm)

on the University of Florida campus After air-drying, the non-contaminated soil was spiked with a Na2HAsO4 solution and incubated for one week to produce an As spiked contaminated soil (ASC) that contained 125 mg

As kg 1dry soil Two composts used in this study were municipal solid wastes (MSW) and Biosolids (BS) which were supplied by the Sumter County Composting Facility and the Palm Beach Authority Composting Facility in Florida, respectively Phosphate rock [PR,

Ca10(PO4)6F2 (CaCO3)x, < 60 mm] was obtained from the PCSPhosphate company (White Springs, FL) Phosphate rock was chosen as the P source for the treatment since it would provide a long-term supply of

P with a low risk of P leaching due to its low solubility Selected properties of soils, composts, and phosphate rock are provided inTable 1

2.2 Soil treatments Dried MSW and BS composts were sieved to a <

2-mm diameter and were mixed with the CCA and ASC soils at a ratio of 50g kg 1soil PR was fully with the soils at a ratio of 15g kg 1soil In addition, Osmocote1

extended time release fertilizer (Scotts-Sierra Horti-cultural Products Co., Marysville, OH) was mixed in as

a base fertilizer at 1g kg 1soil (Tu and Ma, 2002) 1.5

kg of soil containing diﬀerent amendments was placed into each pot (2.5 l, d=15 cm) The three replicates of each amendment were done in a completely randomized factorial design The soils without PR or compost amendments were used as the control

2.3 Greenhouse experiment Fern seedlings were propagated in the lab and trans-ferred, one to a pot, at the 5–6 frond stage (Tu and Ma,

2002) Soil moisture content was maintained at ﬁeld

Trang 3

capacity by periodically weighing the pots and adding

water to compensate for any weight loss The

experi-ment was conducted in a greenhouse at 23–25 C with

an average photosynthetically active radiation at 825

mmol m 2s 1 Pots were randomized on the greenhouse

bench and their positions were changed every 4 weeks to

minimize variations in the micro environments

Soil samples were collected at 0, 2, 5, and 12 weeks by

using a small core made from 10-ml polypropylene

syr-inge The collected soils were air-dried and passed

through a 2-mm sieve Ferns were harvested at the end

of the experiment (12 weeks) After being washed

thor-oughly with tap water and then with deionized water,

the ferns were separated into above ground (fronds) and

below ground (roots) Biomass was measured on a

dry-weight basis after being dried at 65C for 96 h The dry

plant samples were ground into ﬁne powder by using a

tissue mill before acid digestion

2.4 Speciation of soluble As in soil solution

Speciation of As in the soil solution was performed at

the time of plant harvest (12 weeks) Approximately 150

g of each soil at ﬁeld capacity was centrifuged in a

Teﬂon cup at 27 500 g and 25C for 20 min to extract

the soil solutions (Dahlgren et al., 1997) These

solu-tions were then ﬁltered through a 0.20-mm acetate

membrane for total As, As(V), and As(III) analysis

Triplicates were run for each treatment

2.5 Sequential extraction of As in soils

Soil samples were extracted using the sequential

extraction procedure of arsenic (Onken and Adriano,

1997) The procedure separated As into ﬁve operationally

deﬁned fractions: water-soluble and exchangeable As

(WE–As), aluminum bound As (Al–As), iron bound As

(Fe–As), calcium bound As (Ca–As), and residue As

(RS–As) Extractants used in the ﬁve fractions were 1

mol l 1NH4Cl, 0.5 mol l 1NH4F, 0.1 mol l 1NaOH,

0.25 mol l 1HSO , and 1:1 HNO /H O, respectively

One gram of soil was sequentially extracted with 20 ml

of each extraction solution Between each extraction the soil was washed twice with 25 ml of saturated NaCl Each treatment was run in triplicate The arsenic recov-ery was determined by summing the As present in all extracts and comparing that to the total As The results showed satisfactory recoveries of 91–121% The accu-racy of the sequential extraction was evaluated by ana-lyzing Standard Reference Material of 2710 (NIST, Gaithersburg, MD)

2.6 Column leaching experiments

At the end of the greenhouse experiment (week 12), soil samples were collected from all treatments, both with and without ferns After being air-dried, the soils were packed into 60 ml columns (d=2.5 cm), and the soil bulk density was determined to be 1.17–1.32 g ml 1 Columns were run in triplicate for each treatment Deionized water was introduced according to the upward ﬁlling/downward leaching procedure (Peryea

col-lected for both dissolved organic carbon (DOC) and As analyses

2.7 Chemical analysis Soil pH was determined using a 1:1 ratio of soil to deionized water after 24 h of equilibration DOC was determined by using total organic carbon analyzer (TOC-5050A, Shimadzu) Plants and soils were digested using HNO3/H2O2 Hot Block Digestion System (USEPA Method 3050) Arsenic was determined using a graphite furnace atomic absorption spectrometer (GFAAS, Perkin-Elmer SIMMA 6000, Norwalk, CT) Elemental analysis followed an EPA approved QA/QC plan which included a blank, duplicate, and spiked sample in addition to a SRM per 20 samples Quality control samples included Standard Reference Materials

1547 (Peach Leaves) and 2710 Montana Soil (US NIST, MD) Phosphorus analysis was carried out using a

Table 1

Selected physicochemical properties of the soil, composts, and phosphate rock used in this study

(cmol kg 1 )

OC b (%) Sand (%) Silt (%) Clay (%) Total As

(mg kg 1 )

WS–As c

(mg kg 1 )

a Cation exchange capacity.

b Organic carbon.

c Water–soluble As, extracted with deionized water for 1 h at a ratio of liquid/soil=10.

d CCA, chromated–copper–arsenate; ASC, As spiked contaminated; MSW, municipal solid waste; BS, biosolid; PR, phosphate rock.

e Not determined.

Trang 4

modiﬁed molybdenum blue method (Carvalho et al.,

1998) This method eliminated the interference of

arse-nate with P determination by reducing arsearse-nate to

arsenite with L-cysteine As(V) and As(III)

determina-tions were performed using the method of Carvalho et

per-formed by both with and without the cysteine reduction

of As(V) The diﬀerence between these two results yields

the As(V) concentration As(III) was found by

sub-tracting As(V) concentration from the total As result

obtained by GFAAS

2.8 Data analysis

All results are expressed as an average of three

repli-cates, and treatment eﬀects were determined by analysis

of variance according to the general linear model

pro-cedure of the statistical analysis system (SAS Institute

Inc.) Diﬀerences among the treatment means were

separated by least signiﬁcant diﬀerence (LSD)

Sig-niﬁcance was tested at the 0.01 and 0.05 probability

levels

3 Results and discussion

3.1 Properties of the soil and amendment materials

The two soils used showed a signiﬁcant diﬀerence of

1.5 pH units, with the CCA soil being neutral (pH

7.0) and the ASC soil being acidic (pH 5.5)

(Table 1) Total As concentrations in the test soils were

signiﬁcantly higher (125–136 mg kg 1) than the average

background of 0.4 mg kg 1for Florida soils (Chen et

al., 1999) Although the two soils contained a similar

amount of total As, water-soluble As (WS–As) in the

ASC soil was ﬁve times greater than that in the CCA

soil (Table 1) The high level of water soluble As in the

ASC soil was attributed to the spiking of As into the

soil, in which As was predominantly associated with the

labile exchangeable and aluminum oxide fractions

( 80% of total As) On the other hand, in the CCA,

soil As was mainly present in the stable Fe–As and Ca–

As fractions ( 80% of the total As) (Fig 1) Phosphate

rock and the two composts had neutral pH levels ( 7)

The two composts contained > 50% organic carbon with

more organic carbon in the biosolids Arsenic

concentra-tions in both composts and PR were negligible,

com-pared with that in the CCA and ASC soils (Table 1)

3.2 Eﬀects of soil amendments on soil pH, DOC, and

water soluble As

Addition of MSW, BS composts or PR had no

sig-niﬁcant eﬀects on the soil pH (P < 0.01) (Fig 2a and b)

No significant change in pH of the CCA soil was prob-ably due to the similar pH of the soil and each of the amendments The application of the neutral pH amendments increased pH of the acidic ASC soil at first However, there was no significant difference of pH between the control and amended soils after the 2-week equilibration (Fig 2a and b) As expected, amending the soil with PR had no effect on DOC in both the CCA and ASC soils However, both composts increased the DOC in both soils with more pronounced increase observed in the BStreatment (Fig 2c and d) In addi-tion, the CCA soil contained more DOC than the ASC soil although the original OC in the ASC soil was dou-ble that found in the CCA soil (Table 1) This is possi-bly due to high pH in the CCA soil tending to dissolve more organic matter from the composts (Zhou and

mineralization, adsorption, and volatilization of the organic matter in the soils

The water-soluble arsenic (WS–As) was signiﬁcantly elevated in the CCA soil after soil amendments (P < 0.05) (Fig 3a) Phosphate and arsenate exhibit similar physicochemical behavior and compete directly for sorption sites on soil particles (Davenport and

As-con-taminated soils induced arsenate replacement through competitive anion exchange (Peryea, 1998), thereby enhancing As release into the soil solutions Also, the increased DOC may compete for anion adsorption sites The increased organic matter coupled with neutral pH may favor microbial activity which may lower the soil redox potential (Turpeinen et al., 1999) This situation is favorable for the reduction of As(V) to As(III), and a subsequent increase in As mobility (Turpeinen et al.,

1999) At the end of this experiment (12 weeks), the

Fig 1 Arsenic distribution in the CCA and ASC soils WE–As, water-soluble and exchangeable; Al–As, As associated with Al; Fe–As,

As associated with Fe; Ca–As, As associated with Ca; Rs–As, residual As.

Trang 5

CCA–compost soils had up to 24.2% of soluble As in

the soil solution present as As(III), as compared to

<10% in the control and the phosphate-amended soils

(Table 2) Pongratz (1998) reported that the reduction

of As(V) to As(III) occurred as a biotic process in

anaerobic environments Organic material from

com-posts could have provided favorable conditions for As

reduction Also, it could have provided an energy

source for the micro-organisms which are potentially

involved in arsenic transformation (Balasoiu et al.,

2001)

Similarly, phosphate amendment signiﬁcantly

increased WS–As (P < 0.05) in the ASC soil at 12 weeks

although WS-As was less than in the control within ﬁrst

4 weeks (Fig 3b) However, compost treatments

reduced the WS-As compared with the control (Fig 3b)

It is possible because As may be adsorbed on the

organic matter of the composts in acidic ASC soil

(pH=5.45) It has been reported that oxyanion

adsorp-tion was enhanced in the presence of organic matter as

pH decreases (Sposito, 1984).Xu et al (1991)reported

that acidiﬁcation and organic matter addition reduced arsenic mobility with arsenic adsorption reaching a maximum at around pH 5 for As (V) No net transfor-mation of As from As (V) to As (III) occurred in the compost-treated ASC soil (Table 2) It is possible that such a high amount of water-soluble arsenic ( 30 mg

kg 1) in the ASC soil could have inhibited the microbial metabolism (Turpeinen et al., 1999), showing less pos-sibility of As(V) transformation into more available As(III) Therefore, the reduction of As mobility in the ASC soil may be attributed to arsenic adsorption 3.3 Soil As redistribution

Arsenic in the CCA soil was mainly associated with

Ca (56.0%), while Al–As (50.5%) was the predominant form of As in the ASC soil (Table 3) At planting (0 week), soil amendments decreased non-labile As frac-tions of Fe–As and Ca–As, but increased water-soluble and exchangeable As (WE–As) and Al–As in the CCA soil For the ASC soil, however, treatments decreased

Fig 2 Soil pH (a and b) and DOC (c and d) in the CCA (a, c) soil and ASC (b, d) soil samples after compost and phosphate treatments as a function of time CCA, chromated–copper–arsenate, ASC, As spiked contaminated, DOC, dissolved organic carbon; MSW, municipal solid waste;

BS, biosolid; PR, phosphate rock.

Trang 6

WE-As, while Fe–As Ca–As and RS–As were

sig-niﬁcantly elevated

When the ferns were harvested (week 12), the CCA

soil As concentrations in each fraction of the control

and treated soils had decreased with time, especially in

Al–As and Fe–As These two fractions had As decreases

of 11.7 to 34% and 8 to 40%, respectively, when com-pared with the concentrations at planting (Table 3) This probably indicates that As uptake by the fern ori-ginated mainly from these two fractions, with the greatest contribution coming from the Fe–As It can be assumed that the displacement of As by P readily occurred on the surface of the Fe particles and that Fe was readily reduced in the anaerobic soil condition induced by compost addition, thus releasing As for the fern uptake The ASC soil showed a signiﬁcant decrease (P < 0.05) in As concentration in the ﬁrst two fractions

of WE–As and Al–As with time in both the control and the treated soils As expected, the greatest reduction of WE–As occurred in the compost treatments by up to 20.2% after 12 weeks However, Ca–As and RS–As increased with time in the ASC soil This may be par-tially explained by As aging immobilization in the As-spiked ASC soil Nevertheless, this large reduction of WE–As may imply that the fern plant took up As mainly from the WE–As fraction of the ASC soil It should be pointed out that the sequential extraction procedure was only used here to represent successively more recalcitrant forms of arsenic since these fractions

do not necessarily represent speciﬁc discrete forms 3.4 Arsenic uptake and accumulation in the fern plants

are highly tolerant of arsenic and can survive in a soil containing up to 500 mg As kg 1, which was spiked in the soil as Na2HAsO4 For this study, the ferns grew well in the ASC soil with 125 mg As kg 1soil Fronds accumulated up to 5600 mg As kg 1 dry plant weight after 12 weeks (Fig 4), further demonstrating the As-hyperaccumulating capability of Chinese brake fern reported byMa et al (2001)

The PR treatment enhanced As uptake by the Chinese brake fern, with frond concentrations increasing by 256% and 15.4% in the CCA and ASC soils, respec-tively (Fig 4), when compared to the control.Otte et al (1990)reported that U dioica grown in a soil containing

75 mg As kg 1soil took up more arsenic in the presence

of P, most likely via competitive desorption where both

Table 2

Speciation of soluble arsenic in the soil solutions after the fern plants were harvested at 12 weeks

Soluble As (mg l 1 ) in the CCA soil solution Soluble As (mg l 1 ) in the ASC soil solution

Control 5.69 0.11b a 5.13 0.16b 0.56 0.13b 9.68b 30.2 1.17b 28.6 2.31a 1.61 0.27a 5.33a MSW b 7.28 0.33a 5.82 0.28b 1.46 0.27a 20.0a 26.2 4.70c 24.7 2.31b 1.52 0.72a 5.80a BS6.94 0.32a 5.26 0.21b 1.68 0.31a 24.2a 22.8 2.69c 21.3 1.74b 1.51 0.21a 6.62a

PR 7.40 0.48a 6.72 0.62a 0.68 0.17b 8.61b 35.8 2.92a 23.8 2.17b 1.95 0.45a 5.45a

a Mean standard deviation (n=3), values ending in the same letter within each column are not signiﬁcantly diﬀerent (P < 0.05).

b CCA, chromated–copper–arsenate; ASC, artiﬁcially As contaminated; MSW, municipal solid waste; BS, biosolid; PR, phosphate rock.

Fig 3 Water-soluble As in the CCA soil (a) and ASC soil (b) after

compost and phosphate treatments as a function of time CCA,

chro-mated–copper–arsenate, ASC, As spiked contaminated, DOC,

dis-solved organic carbon; MSW, municipal solid waste; BS, biosolid; PR,

phosphate rock.

Trang 7

elements compete for the same adsorption sites in the soil and root surfaces, which is expected due to their chemical similarity.Peryea (1998)demonstrated that the applica-tion of phosphorus fertilizer to arsenic-contaminated soils resulted in the displacement of about 77% of the total arsenic in the soil Previous studies showed that any eﬀect P has on As uptake by plants is liked directly with the growth media (Jacobs and Keeney, 1970; Meharg et al., 1994; Woolson et al., 1973) In a hydro-ponic system, 15 mg l 1can reduce As uptake by 75%

in both tolerant and non-tolerant plant genotypes of Holcus lanatus L (Meharg and Macnair, 1991) Simi-larly, Rumburg et al (1960) reported that increasing concentrations of P decreased the amount of arsenate removed by oats from a nutrient solution For Indian mustard (Brassica juncea), phosphorus addition resulted

in a reduction of As uptake by 55–72% over the control (Pickering et al., 2000) However, in the soil system, phosphate addition increases available arsenic by repla-cing adsorbed arsenic, thus resulting in elevated arsenic uptake (Jacobs and Keeney, 1970; Turpeinen et al.,

1999) It is not surprising that the diﬀerences of As availability occurred between soil and hydroponic sys-tems since other soil parameters (Eh, pH) also inﬂuence

As solubility or mobility (Meharg and

between P and As in the fern plants (r2=0.83, P < 0.05) Similar results were reported by Komar (1999) with a positive correlation between plant P and As concen-tration in Chinese brake fern Increasing cell phospho-rus levels reduced formation of the arsenate-substituted ATP analogue and therefore increased overall arsenic tolerance (Meharg et al., 1994) The phosphate uptake system, by which arsenic is taken up (Meharg et al.,

1994), is induced under a low phosphate status like in

Fig 4 Root and frond arsenic concentrations in the Chinese brake

fern grown in the CCA soil (a) and ASC soil (b) at 12 weeks CCA,

chromated–copper–arsenate, ASC, As spiked contaminated, MSW,

municipal solid waste; BS, biosolid; PR, phosphate rock.

Table 3

Arsenic concentrations (mg kg 1 soil) in each soil fraction at planting and harvest

At planting (week 0)

At harvest (week 12)

c CCA, chromated–copper–arsenate; ASC, artiﬁcially As contaminated; MSW, municipal solid waste; BS, biosolid; PR, phosphate rock.

a WE–As, water-soluble and exchangeable; Al–As, aluminum bound As; Fe–As, iron bound As; Ca–As, calcium bound As; RS–As, residue As.

b Mean (n=3), values ending in the same letter within each column are not signiﬁcantly diﬀerent (P < 0.05).

Trang 8

some angiosperms and fungi Synergistic eﬀects of P

addition to As contaminated soils may be another

explanation for the enhancement of As uptake by

Chi-nese brake fern The reason for this synergistic eﬀect is

unclear, but may be related to P nutrition Since As can

replace P in plants, but is unable to carry out the role of

P in energy transfer, the plants reacts as if there is a P

deﬁciency Thus, as plant As increases, the plants reacts

by increasing P uptake (Burlo et al., 1999;

Carbonell-Barrachina et al., 1998)

The eﬀects of composts varied in the two soils Both

composts increased As uptake from the CCA soil, but

decreased As uptake from the ASC soil Enhanced As

uptake from the CCA soil is related to the WS–As

increase (Fig 3a) and the transformation of As(V) to

As(III) (Table 2) As(III) increased from 9.7 to 20% and

24.2% of the As in soil solution for the MSW and BS

treatments, respectively Heeraman et al (2001)

sug-gested that WS–As is a good predictor for plant uptake

of As Sadiq (1986) also indicated a positive relation

between water extractable As and plant uptake in corn

It has been observed that As(III) has a higher

avail-ability to the plants than As(V) (Carbonell-Barrachina

et al., 1998; Marin et al., 1992) Contrary to the CCA

soil, compost amendments reduced WS–As in the ASC

soil (Fig 3b), resulting in the reduction of As uptake by

the fern (Fig 4b)

The Chinese brake ferns accumulated much more As

from ASC soil than from CCA soil in all treatments

(Table 4) because the ASC soil contained more As in the

bioavailable fractions (WS–As, Al–As) than the CCA

soil (Fig 1) For the CCA soil, compost amendments

enhanced but were not signiﬁcantly (P < 0.05) diﬀerent

from As accumulations in the controls (Table 4),

whereas phosphate treatment had the greatest plant

arsenic accumulation, at more than three times that of

the control After 12 weeks, PR treatment signiﬁcantly

increased arsenic removal from 2.56 up to 8.27%

Con-trary to the CCA soil, composts signiﬁcantly reduced As accumulation from ASC soil The PR treatment increased As accumulation (Table 4) After 12 weeks, plants with compost amendments removed < 8%As from ASC soil, less than the 11.9% removed from the control PR showed a signiﬁcant amount of arsenic removal from the ASC soil (14.4%) Most of the arsenic ( > 90%) taken up by the fern was accumulated in the fronds (Table 4)

It should be pointed out that arsenic volatilization may have occurred in the compost amended CCA soils,

as less than 84% of As was recovered (Table 5) Up to 16% As loss from the soils may be attributable to microbially-mediated arsenic volatilization in the CCA soil Loss of As from solution in reduced soils has long been attributed to arsenic volatilization as arsine gas (Onken and Adriano, 1997) It has been proven that application of organic composts reduces soil redox potential, especially when the soil pH is higher (Onken and Adriano, 1997) In such an environment, arsenate

is easily reduced to arsenite and then methylated to form methylarsonic acid These As compounds may further be reduced to methylarsines that volatilize to the atmosphere (Sadiq, 1997) Soil microbes have been shown to produce volatile arsenicals by a reductive pathway from inorganic and methylated forms of As

added DSMA-74As to a soil system and measured a loss

of 74As The loss of74As from the reduced soil system was attributed to the gaseous evolution of arsine, though no arsine was detected In our experiments, up

to 12% arsenic loss was also observed in compost-amended CCA soil even without a fern present (data not shown) No signiﬁcant change in arsenic was observed in the PR-treated soils This further supported the ideas that compost induced transformation of arse-nate to arsenite, which was further transformed into volatile arsenic

Table 4

Arsenic accumulation and distribution in Chinese brake ferns grown in the CCA and ASC soils

% of soil As

CCA soil a

ASC soil

a CCA, chromated-copper-arsenate; ASC, As spiked contaminated; MSW, municipal solid waste; BS, biosolid; PR, phosphate rock.

b Mean standard deviation (n=3), values ending in the same letter within each column are not signiﬁcantly diﬀerent (P < 0.05).

Trang 9

3.5 Arsenic leaching in soils

The eﬀects of soil amendments on As leaching in soils

were studied using column experiments Eﬄuent As

concentrations reached steady-state levels within 10

pore volumes (data not shown) The ASC soil had

greater leaching of As than the CCA soil at the end of

12 weeks (Table 6) It is because ASC soil As was

pre-dominantly associated with exchangeable and

alumi-num oxide fractions ( 80% of total As), while the

CCA soil contained approximately 16% of the total As

in these fractions (Fig 1)

Without a fern to absorb soil solution As, soil

amendments signiﬁcantly increased As leaching in the

CCA soil The greatest eﬀect was with the compost

treatments that had > 50% increase when compared

with the controls As a result of arsenic transformation

to As(III) and competitive desorption with DOC,

arsenic leaching from the CCA soil was enhanced in the

compost amended soils with the absence of a fern plant

(Table 6) In the experiment ofTurpeinen et al (1999)

there was clear evidence that microbes enhance As

leaching in soil In formaldehyde-treated soil samples

there was no growth in microbial plate counts and arsenic leaching was greatly reduced Also,Ahmann et

al (1997)reported that in autoclaved or formaldehyde-treated samples arsenic mobilization (or release) was much lower than in the control samples Organic matter from composts provides a carbon source for microbes

to enhance bioleaching in addition to promoting their growth Chirenje et al (2002) noted that arsenic was related to the DOC in the effluents of a column leaching experiment Similar to this study, arsenic concentrations were positively correlated to DOC in the effluents (data not shown) as the DOC increased after compost addi-tion Compost amendments in this study increased arsenic leaching, corresponding to significantly higher DOC leaching As hypothesized, uptake by ferns reduced As leaching with the biggest decline in the PR treatment (Table 6) The PR treatment with ferns decreased 58.5% of As leaching in the CCA soil, respectively, compared with that without ferns

Displacement of As by P from the sorption sites increased arsenic mobility in the CCA soil when there is

no fern root to absorb the As from the soil solution (Table 6) This is consistent with the mechanism of P-enhanced release of As in the soil and subsequent pro-motion of As movement through the soil by competition

of dissolved As and P for ion adsorption sites ( Daven-port and Peryea, 1991) reported that phosphate addition signiﬁcantly increased the amount of As leached from the soil Nevertheless, in the presence of Chinese brake ferns, phosphate showed the biggest decrease in As leaching as compared to the other treatments (Table 6) This is most likely attributable to the high As uptake For the ASC soil, soil amendments reduced As leach-ing regardless of fern presence with the exception of phosphate application which actually increased slightly As leaching without planting Arsenic aging immobilization may be responsible for this reduction in the ASC soil since arsenic spiked was equilibrated with soil for only 1 week prior to treatment with compost and phosphate rock

Table 5

A mass balance of As in the CCA soil an AAC soil (mg pot 1 )

Soil As (week 12) Fern As (week 12) Soil+Fern (week 12) Original (week 0) % (Sum/total) CCA soil a

AAC soil

a CCA, chromated-copper-arsenate; ASC, As spiked contaminated; MSW, municipal solid waste; BS, biosolid; PR, phosphate rock.

b Mean standard deviation (n=3 values ending in the same letter within each column are not signiﬁcantly diﬀerent (P < 0.05).

Table 6

Cumulative mass of soluble As leached from soil columns (10 pore

volumes of leaching elution) constructed from treatments after the end

of the 12 week study

CCA soil mg As kg 1 ASC soil mg As kg 1

With fern Without fern With fern Without fern

Control a 14.6 1.23a b 20.7 3.27c 16.5 1.83a 40.5 4.27a

MSW 12.4 0.98b 31.5 2.43a 12.4 0.31b 31.5 3.21b

BS14.4 2.31a 33.2 3.21a 11.5 0.69b 29.6 2.33b

PR 11.6 1.93b 28.0 1.72b 10.1 1.21b 41.7 3.11a

a CCA, chromated-copper-arsenate; ASC, As spiked contaminated;

MSW, municipal solid waste; BS, biosolid; PR, phosphate rock.

b Mean standard deviation (n=3), values ending in the same letter

within each column are not signiﬁcantly diﬀerent (P < 0.05).

Trang 10

With time, As moves to mineral forms which are in

equi-librium with the present soil environment However, the

greatest reduction (75.7%) of As leaching was observed in

the phosphate amendment in the presence of the fern

4 Conclusions

Phosphate addition signiﬁcantly enhanced As uptake

by Chinese brake fern, with frond As concentrations

increasing up to 265% as compared with the control

After 12 weeks, plants grown in phosphate-amended

soil removed up to 8.27% of the As from the CCA soil

and 14.4% from the ASC soil The enhanced uptake of

As in the phosphate treatment was attributable to the

displacement of soil As by P from adsorption sites into

the soil solution The eﬀect of compost on As uptake

depended on soil properties (e.g pH) In the CCA soil

with a neutral pH, compost treatments may have

induced an anaerobic environment in the soil, which

was favorable for the conversion of As (V) to the mobile

As (III), thereby facilitating As uptake by the fern In

contrast, As adsorption onto organic matter applied in

acidic soil may be responsible for the decrease of As

uptake in the ASC soil after treatment with compost

The Chinese brake fern took up As mainly from Fe–As

and Ca–As fractions in CCA soil, and from WE–As

fraction in ASC soil Both compost and phosphate

amendments increased As leaching from CCA soil in

the absence of the fern, but decreased in the presence of

the fern For the ASC soil, both treatments reduced As

leaching regardless of the presence of the fern The

results indicate that growing Chinese brake fern with

the application of phosphate rock is more eﬀective for

remediating As-contaminated soils

Acknowledgements

This research was supported by the Florida

Depart-ment of EnvironDepart-mental Protection (Contract No

HW446) The authors would like to thank Thomas

Luongo for his assistance in chemical analysis Two

anonymous reviewers were gratefully acknowledged for

the valuable comments that improved the manuscript

References

Ahmann, D., Krumholz, L.R., Hemond, H.F., Lovley, D.R., Morel,

F.M.M., 1997 Microbial mobilization of arsenic from sediments of

the Aberjona Watershed Environ Sci Technol 31, 2923–2930.

Akins, M.B., Lewis, R.J., 1976 Chemical distribution and gaseous

evolution of arsenic-74 added to soils as DSMA-74 arsenic Soil Sci.

Soc Am J 40, 655–658.

Balasoiu, C.F., Zagury, G.J., Deschenes, L., 2001 Partitioning and

speciation of chromium, copper, and arsenic in CCA-contaminated

soils: inﬂuence of soil composition Sci Total Environ 280, 239–255.

Burlo, F., Guijarro, I., Barrachina, A.A.C., Vlaero, D., 1999 Arsenic species: eﬀects on uptake and accumulation by tomato plants J Agric Food Chem 47, 1247–1253.

Carbonell-Barrachina, A.A., Aarabi, M.A., Delaune, R.D., Gambrell, R.P., Patrick, J.W.H., 1998 Arsenic in wetland vegetation: Avail-ability, phytotoxicity, uptake and eﬀects on plant growth and nutrition Sci Total Environ 217, 189–199.

Carvalho, L.H.M., Dekoe, T., Tavares, P.B., 1998 An improved molybdenum blue method for simultaneous determination of inor-ganic phosphate and arsenate Ecotoxicology and Environmental Restoration 1, 13–19.

Chen, M., Ma, L.Q., Harris, W.G., Hornsby, A., 1999 Background concentrations of 15 trace metals in Florida soils J Environ Qual.

28, 1173–1181.

Chirenje, T., Rivero, C., Ma, L.Q., 2002 Leaching of As and Cr in wood-ash-amended soil columns Soil and Sediment Contamination

11, 359–375.

Christen, K., 1999 Arsenic standard for drinking water too high, National Research Council says Environ Sci Tech A, 188 Dahlgren, R.A., Percival, H.J., Parﬁtt, R.L., 1997 Carbon dioxide degassing eﬀects on soil solutions collected by centrifugation Soil Sci 162, 648–655.

Davenport, J.R., Peryea, F.J., 1991 Phosphate fertilizers inﬂuence leaching of lead and arsenic in a soil contaminated with lead arse-nate Water, Air and Soil Pollution 57-58, 101–110.

Heeraman, D.A., Claassen, V.P., Zasoski, R.J., 2001 Interaction of lime, organic matter and fertilizer on growth and uptake of arsenic and mercury by Zorro fescue (Vulpia myuros L.) Plant and Soil 234, 215–231.

Hingston, J.A., Collins, C.D., Murphy, R.J., Lester, J.N., 2001 Leaching of chromated copper arsenate wood preservatives: a review Environ Pollut 111, 53–66.

Jacobs, L.W., Keeney, D.R., 1970 Arsenic-phosphorus interaction on corn Communications in Soil Science and Plant Analysis 1, 85–93 Johnson, D.L., Pilson, M.E.Q., 1972 Spectrophotometric determina-tion od arsenite, arsenate, and phosphate in natural waters Analy-tica Chimica Acta 58, 289–299.

Komar, K.M 1999 Phytoremediation of Arsenic Contaminated Soils: Plant Identiﬁcation and Uptake Enhancement MS, University of Florida, Gainesville.

Lombi, E., Zhao, F.J., Dunham, S.J., McGrath, S.P., 2001 Phytor-emediation of heavy metal-contaminated soils:Natural hyper-accumulation versus chemically enhanced phytoextraction J Environ Qual 30, 1919–1926.

Ma, L.Q., Komar, K.M.M., Tu, C., Zhang, W., Cai, Y., Kennel-ley, E.D., 2001 A fern that hyperaccumulates arsenic Nature

409, 579.

Marin, A.R., Masscheleyn, P.H., Patrick Jr., H.W., 1992 The inﬂu-ence of chemical form and concentration of arsenic on rice growth and tissue arsenic concentration Plant and Soil 139, 175–183 Meharg, A.A., Hartley-Whitaker, J., 2002 Arsenic uptake and meta-bolism in arsenic resistant and non resistant plant species New Phytol 154, 29–43.

Meharg, A.A., Macnair, M.R., 1991 Uptake, accumulation and translocation of arsenate in arsenate-tolerant and non-tolerant Holcus lanatus L New Phytol 117, 225–231.

Meharg, A.A., Naylor, J., Macnair, M.R., 2002 Phosphorus nutrition

of arsenate-tolerant and nontolerant phenotypes of velvetgrass J Environ Qual 23, 234–238.

Onken, B.M., Adriano, D.C., 1997 Arsenic availability in soil with time under saturated and subsaturated conditions Soil Sci Soc.

Am J 61, 746–752.

Otte, M.L., Rozema, J., Beek, M.A., Kater, B.J., Broekman, R.A.,

1990 Uptake of arsenic by estuarine plants and interaction with phosphate, in the ﬁeld (Rhine Estuary) and under outdoor experi-mental conditions Sci Total Environ 97/98, 839–854.

Peryea, F.J., 1998 Phosphate starter fertilizer temporarily enhances

Định dạng
Số trang	11
Dung lượng	304,83 KB